1. Field of the Invention
[Technical Field]
The present invention relates to a particle detection apparatus for detecting fine particles floating in the air, such as dust, pollen and smoke, and a particle detection method used therefor.
2. Description of Related Art
[Background Art]
In recent years, as the number of patients suffering from allergy such as hey fever increases, there is a growing concern on indoor conditions. Therefore, in relation to products such as an air cleaner and an air conditioner, there is a demand for detecting, at a high sensitivity, fine particles such as dust, pollen and cigarette smoke, which may present in an environment where those products are used.
In many buildings, air conditioning facilities are equipped to keep indoor conditions at a predetermined level or above. In order to maintain predetermined indoor conditions, regulations are imposed upon those facilities by laws and ordinances so that an amount of floating dust be kept at a predetermined level or below. In recent years, on the other hand, it is desired to efficiently operate air conditioning facilities from a viewpoint of energy saving. Accordingly, there is a strong demand for means for measuring an amount of floating dust more accurately.
Conventionally, there are known various sensor devices and detection methods for detecting fine particles such as dust, pollen and smoke floating in a room.
As one example, an apparatus having an intake function is known, according to which a gas to be measured is taken from the outside, light is illuminated from an internal LED to the gas to be measured, and light scattered by particles floating in the gas is detected for determining existence of the particles (Patent Document 1).
There is also known an apparatus for detecting particles from changes in polarization state of transmitted light, rather than measurements of scattered light (Patent Document 2). In this apparatus, light to be illuminated is pulsed to separately detect dust and smoke. Since smoke is composed of very fine particles (particle diameter: 0.01 micrometer to several micrometers), it stays in the air for a relatively long period of time. On the other hand, dust or pollen is larger in particle size and heavier. Therefore, they drift through the air, but have a higher falling speed. Accordingly, when a light pulse is applied, a sensor output changes gradually when smoke enters into the apparatus. However, when dust enters into the apparatus, the sensor output changes rapidly compared to the case where smoke enters, and it is possible to distinguish dust from smoke. In both cases, dust and smoke are identified from information on temporal changes.
Further, a sensor apparatus for detecting pollen, wherein a laser is used to distinguish pollen from other fine particles is known (Patent Document 3). In that apparatus, a laser and two photodetectors are used. First, laser light is illuminated to a gas to be measured, and two scattered light components, i.e., vertical and horizontal polarized light components are detected regarding the illuminated laser light, and an output therefrom enables identification between pollen and other particles. Based on differences in polarization states of the scattered light, pollen is distinguished from other fine particles.
[Patent Document 1] Japanese Patent Laid-Open Publication No. 2000-356,583
[Patent Document 2] Japanese Patent Laid-Open Publication No. 2001-83,079
[Patent Document 3] Japanese Patent Laid-Open Publication No. 2004-125,602